1. Field of the Invention
This invention relates to power supplies for life assisting devices, in general, and to an implantable power supply for use with an implantable defibrillator, in particular.
2. Description of the Prior Art
Great strides are presently being made to develop an automatic, fully implantable ventricular defibrillator. See, for example, U.S. Pat. Nos. Re. 27,652 and Re. 27,757, where the first concept of the automatic implantable ventricular defibrillator is described. Recent advances have also been made in enhancing the reliability of fibrillation detectors. In this latter regard, see copending U.S. Pat. No. 4,184,493 and U.S. Pat. No. 4,202,340, each filed on Feb. 15, 1978. Furthermore, as outlined in copending U.S. Pat. No. 4,164,946, filed on May 27, 1977, steps have been taken to improve the reliability of the implanted defibrillator by the provision of circuitry which interrogates the implanted electronics to verify proper operation before a defibrillation shock is delivered.
Notwithstanding the substantial steps which have been taken to develop the automatic, fully implantable defibrillator and to insure the operation of the sensing and defibrillating circuitry, it must not be forgotten that the implantable defibrillator is in its infancy.
In an implantable defibrillator, a fibrillation detecting circuit, operatively associated with the heart of a recipient, detects a fibrillation episode, and, in response thereto, activates a power inverter. When activated, the power inverter directs energy from an energy source, such as a battery, to an energy storage device, such as a storage capacitor. When the storage capacitor is fully charged, additional circuitry contained in the defibrillator releases the energy stored in the storage capacitor into the heart of the recipient as a defibrillating shock.
In the implantable defibrillator discussed above, the detection circuit and the charging circuit are powered by two extended-life batteries connected in series. Still, it is possible for one of the batteries to become discharged, while the other battery may still be far from depleted. In such an instance, the prior circuit design would not permit continued operation of both the detection and the charging circuits.
The problem of battery failure is also present in the field of cardiac pacemakers and other implantable body organ stimulators. In these other fields, it has been proposed that the battery depletion problem can be overcome by connecting fewer batteries in series, connecting series groups in parallel, using diode "or" connections, and using voltage doubler and tripler circuits for producing sufficient voltage for effective device operation.
None of these alternative arrangements offers a solution to the unique problem associated with implantable defibrillators; namely, that of assuring continued operation of the fibrillation detecting circuit and the power inverter over the full ife of the batteries because the inverter draws several orders of magnitude more current than the detecting circuit.